It's also used to treat infected insect bites, skin ulcers, bed sores and wounds, and to treat and prevent bacterial and parasitic infections.

Metronidazole is only available on prescription.

It comes as a tablet, gel, cream, a liquid you drink or a suppository which is a medicine that you push gently into your anus. It's also given by injection, but this is usually only done in hospital.

2. Key facts

The most common side effects of metronidazole tablets, liquid, suppositories or vaginal gel are feeling or being sick, diarrhoea, and a slight metallic taste in your mouth.

Do not drink alcohol while taking a course of metronidazole tablets, liquid, suppositories or vaginal gel, or for 2 days after finishing treatment. Alcohol can cause side effects such as feeling and being sick, stomach pain, hot flushes, a pounding heartbeat (palpitations) and a headache.

For most infections, you'll start to feel better in a few days but for some it may take longer. When treating rosacea, you may only notice a difference after several weeks.

Metronidazole tablets or suppositories are called by the brand name Flagyl.

Metronidazole cream is called by the brand names Rosiced or Rozex. The gel is called by the brand names Acea, Anabact, Metrogel, Metrosa, Rozex or Zyomet.

3. Who can and can't take metronidazole

Metronidazole can be taken by most adults and children. Metronidazole isn't suitable for some people.

To make sure the tablets, liquid or suppositories are safe for you, tell your doctor if you:

have had an allergic reaction to metronidazole or any other medicines in the past

4. Tablets, liquid or suppositories

Metronidazole tablets, liquid and suppositories are prescribed for a number of infections, including pelvic inflammatory disease. The form your doctor prescribes, the dose and how long you'll need to take the medicine for depends on the type of infection and how serious it is.

Some infections can be treated with a single dose, while others may need a 2 week course. Children's doses are lower and depend on the age or weight of your child. Follow the instructions from your doctor or pharmacist.

Metronidazole tablets should be swallowed whole with a drink of water, after you've eaten some food.

Metronidazole liquid does not need to be taken after food. This medicine comes with a plastic syringe or spoon to help you measure out the right dose. If you don't have one, ask your pharmacist for one. Do not use a kitchen teaspoon as it will not give the right amount.

Your doctor may prescribe metronidazole suppositories if you have difficulty swallowing medicines. Metronidazole suppositories are usually used 3 times a day. Follow the instructions that come in the packaging with your medicine.

If you need to take several doses of metronidazole a day, try to space them evenly. For example, if you take your medicine 3 times a day, this could be first thing in the morning, mid-afternoon, and at bedtime.

How long should I take it for?

It's very important to keep taking metronidazole for as long as your doctor has prescribed it.

Important

Carry on taking this medicine until you have finished the course, even if you feel better. If you stop your treatment early, the infection could come back.

What if I forget to take it?

If you forget to take a dose, take it as soon as you remember, unless it's nearly time for your next dose. In this case, just leave out the missed dose and take your next dose as normal.

Never take 2 doses at the same time. Never take an extra dose to make up for a forgotten one.

If you often forget doses, it may help to set an alarm to remind you. You could also ask your pharmacist for advice on other ways to remember your medicines.

What if I take too much?

Accidentally taking an extra dose of metronidazole is unlikely to harm you or your child.

Speak to your pharmacist or doctor if you're worried or you take more than 1 extra dose.

5. Cream or gel

When metronidazole cream or gel is prescribed for rosacea, you'll normally use it twice a day for about 2 months. Treatment can sometimes last longer. Follow the instructions from your doctor or pharmacist.

If you're using the cream or gel for a skin infection, or infected ulcers or wounds, it's usual to put it on once or twice a day. Follow your doctor or pharmacist's instructions, and continue treatment until
your infection has healed.

How to put it on

Put a thin layer of cream or gel onto the area you're treating and rub it in very gently. Try to avoid getting it into your eyes, as it can sting. If you do get some in your eye, wash it out immediately with cold water.

How long should I use it for?

It's very important to keep using metronidazole cream or gel for as long as your doctor has prescribed it.

Important

Carry on using this medicine until you have finished the course, even if you feel better. If you stop your treatment early, the infection could come back.

What if I forget to use it?

If you forget to use metronidazole cream or gel, put it on as soon as you remember, unless it's nearly time for your next dose. Do not use it more than twice a day unless your doctor tells you to. Then continue to use the cream or gel at the usual time.

What if I use too much?

If you put on too much cream or gel - or if you get some in your mouth - it's unlikely to harm you.

Talk to your pharmacist or doctor if you're worried, or if you or your child accidentally swallow a lot of it.

6. Vaginal gel

For treating bacterial vaginosis, you'll use an applicator to put the metronidazole gel into your vagina. The usual dose is 1 applicator full, every night for 5 nights. It's recommended that you do not use the
gel while having your period.

How to use it

Follow the instructions that come in the packaging along with your medicine. These will tell you how to fill the applicator with gel and put it into your vagina.

Do not have sex while using the vaginal gel.

How long should I use it for?

It's very important to keep using metronidazole vaginal gel for as long as your doctor has prescribed it.

Important

Carry on using this medicine until you have finished the course, even if you feel better. If you stop your treatment early, the infection could come back.

What if I forget to use it?

If you forget to use metronidazole vaginal gel, use it as soon as you remember, unless it is nearly time for your usual dose. Do not use it more than once a night. Then continue to use the gel at the usual time.

What if I use too much?

If you accidentally use too much gel it's unlikely to harm you.

Talk to your pharmacist or doctor if you're worried.

7. Side effects

It's unusual to have side effects when using metronidazole cream or gel. However there can be some common side effects with the tablets, suppositories or vaginal gel.

Do not drink alcohol while taking the tablets or liquid or using the vaginal gel or suppositories. It can give you severe side effects such as feeling or being sick, stomach pain, hot flushes, a pounding heartbeat (palpitations) and a headache. After finishing your treatment, wait for 2 days before drinking alcohol again. This allows the metronidazole to leave your body.

Common side effects of tablets, liquid, suppositories or vaginal gel

Keep taking the medicine, but talk to your doctor or pharmacist if these side effects bother you or don't go away:

feeling sick (nausea)

being sick (vomiting) or diarrhoea

metallic taste in your mouth or a furry tongue

Serious side effects of tablets, liquid, suppositories or vaginal gel

Serious side effects are rare and happen in less than 1 in 1,000 people.

Call a doctor straight away if:

you get yellow skin or the whites of your eyes turn yellow - these can be warning signs of liver or gallbladder problems

you get unexpected infections, mouth ulcers, bruising, bleeding
gums, or extreme tiredness - these can be caused by a blood problem

you have bad stomach pains which may reach through to your back - this can be a sign of pancreatitis

you have blurred or double vision

you have a fever (38C and above) and stiff neck, you're seeing or hearing things that aren't there (hallucinating), feeling confused, unable to cope with bright light or having difficulty speaking - these
can be warning signs of meningitis, or that metronidazole is affecting your brain

8. How to cope with side effects

What to do about:

feeling sick (nausea) - stick to simple meals and do not eat rich or spicy food. You should always try to take your metronidazole after a meal or snack.

being sick (vomiting) or diarrhoea - drink lots of fluids, such as water or squash to avoid dehydration. Take small, frequent sips if you are being sick. Signs of dehydration include peeing less than usual or having dark, strong-smelling pee. If your diarrhoea and vomiting continues for more than 24 hours contact your
doctor for advice. Do not take any other medicines to treat diarrhoea or vomiting without speaking to a pharmacist or doctor.

metallic taste in your mouth or a furry tongue - drink plenty of water and eat plain foods that you usually enjoy. If your tongue is very furry, this could be a sign of thrush - ask your pharmacist or doctor for advice.

9. Pregnancy and breastfeeding

It's generally safe to use metronidazole while you're pregnant or breastfeeding.

If you're breastfeeding, take care when applying metronidazole cream or gel. Make sure you do not accidentally get it on your breasts. If this happens, wash off any cream or gel from your breasts before feeding your baby.

any medicines that you take as a liquid, in case these contain alcohol

Mixing metronidazole with herbal remedies and supplements

There are no known problems with taking herbal remedies and supplements alongside metronidazole. However, some remedies and supplements that come as liquids that you drink may also contain alcohol. Check the list of ingredients or ask the supplier or manufacturer.

Important

For safety, tell your doctor or pharmacist if you're taking any other medicines, including herbal remedies, vitamins or supplements.

11. Common questions

How does metronidazole work?

Metronidazole is an antibiotic. It works by stopping the growth of the bacteria (or parasites) causing the infection.

How long does it take to work?

For most infections, you should feel better within a few days.
With serious swelling (including dental infections), the medicine will start working within a few days but it may take longer before your symptoms start to get better.

For some of the infections that metronidazole is used for, you may only begin to notice an improvement after a week.

When using the cream or gel to treat rosacea, you may have to wait a few weeks before you see any improvement.

It's very important that you keep taking metronidazole until the course is finished. Do this even if you feel better. It will help stop the infection coming back.

What if I don't get better?

Tell your doctor if you still don't feel better 2 or 3 days after
finishing your course of metronidazole. Also tell them if, at any time, you start to feel worse.

However, if metronidazole makes you vomit or have severe diarrhoea (6 to 8 watery poos in 24 hours) for more than 24 hours, your contraceptive pills may not protect you from pregnancy. If this happens, follow the instructions in the leaflet that comes with your contraceptive pills.

Some people get a fungal infection called thrush after taking a course of antibiotics like metronidazole. This is more common if you're using the vaginal gel. It happens because antibiotics
kill the normal harmless bacteria that help to protect you against thrush.

Ask your pharmacist or doctor for advice if this happens to you.

Will it reduce my fertility?

There's no firm evidence to suggest that taking metronidazole will reduce fertility in either men or women. However, speak to a pharmacist or doctor before taking it if you're trying to get
pregnant.

Can I drive or ride a bike?

Metronidazole doesn't usually affect you being able to drive or cycle.

However, very rarely, some people suffer from drowsiness or blurred vision. Do not drive or ride a bike until you stop feeling drowsy and your vision is clear.

Can I drink alcohol with it?

Do not drink alcohol while you're taking metronidazole, including for 2 days afterwards. This gives the medicine time to leave your body.

This is important because metronidazole can react with alcohol to cause a number of side effects. These include feeling and being sick, stomach pain, hot flushes, a pounding heartbeat (palpitations) and a headache.

Is there any food or drink I need to avoid?

You must not have any alcohol (in either your food or drink) while taking metronidazole - and for 2 days afterwards.